Variable Lens System

Abstract

A compact and substantially achromatic optical lens system (100, 200) comprising an electrowetting lens (104, 204) is provided. The optical lens system is using an electrowetting lens in which at least one of the entrance window surface (117, 217) or exit window surfaces (219), being in contact with one of the fluids (112, 212, 113, 213), has a curvature. When the sign of the curvature of that surface has the same sign as the curvature of the meniscus when no voltage is applied, a low building height is achieved. The optical element (104, 204) not only acts as a focussing or zooming device, but that it also acts as an aberration reduction element for the other elements in the optical lens system (100, 200).

Description

FIELD OF THE INVENTION[0001]The present invention relates to an optical lens system using a variable lens comprising a first fluid and a second fluid which are in contact over a meniscus, to an imaging system including such an optical lens system and to a method of designing such a variable lens system and optical imaging system.BACKGROUND OF THE INVENTITON[0002]A variable lens is a device in which one or more properties of the lens can be controllably adjusted, e.g. in which the focal length or the position of the lens can be altered. An optical lens system is used to image an object on to an image sensor. This optical lens system can comprise a variable lens[0003]The general trend in the development of image sensors for camera modules is that they constantly increase in resolution. Starting from the low-resolution sensors such as the 100k-pixels range CIF image sensors and 300k-pixels image sensors, there are presently high-resolution mega-pixel image sensors available. These high...

AI Technical Summary

Benefits of technology

[0019]When using curved surfaces for at least one of the entrance or exit window the surfaces of the optical element may take part in the overall optical design. The curvatures of the windows may be used as extra number of degrees of freedom for the optical design to optimise the optical performance of the optical lens system. This means that the curvatures of the windows may be adapted for correction or reduction of aberrations of other elements in the optical lens system. The optimisation may result in a substantial reduction of optical errors such as distortion and spherical aberration. It also allows a reduction in number of optical elements in the total optical system to achieve the required overall optical quality.

[0022]The position of the electrowetting lens in the first lens group may result in a small diameter electrowetting lens, resulting also in a low building height and a long focal range. The building height can be further reduced when, in the situation that no voltage is applied, the radius of the curvature of the meniscus is having the same sign as the radius of the curvature of the lens surface in contact with the fluid. A low building height is suitable for e.g. camera application, in mobile telephones.

[0023]The stop should preferably be placed close behind or integrated and close to the exit window of the electrowetting lens, when using a small electrowetting lens in the first lens group. This stop can block unwanted reflections in the first lens group, which reflections may otherwise reach the image sensor and result in ghost images.

[0025]As commonly used image sensors, such as mega-pixel image sensors, have a buried sensitive area, the acceptance angle of the imaging beam is limited to about 20 to 25 degrees. This means that in the design of the optical lens system the maximum chief-ray angle with the optical axis of the optical lens system towards the image sensor is preferably lower than this acceptance angle. A field-flattening lens can be arranged between the electrowetting lens and the image sensor to reduce the chief-ray angles as well as to flatten the focal plane.

Problems solved by technology

The known electrowetting lens has limited magnification, field flattening and aberration reduction possibilities due to the limited number of optical surfaces.

As a result, the module is only suitable for low-resolution cameras such as CIF and VGA.

For cameras with for higher resolution sensors such as the 500k-pixel range (S)VGA image sensors, the 1M-pixel range XGA image sensors and mega-pixel devices this is not sufficient.

Due to this location straylight entering the lens system can still reflect from the cylindrical wall of the lens system towards the image sensor, resulting in ghosting.

As a result, in such a design the amount of space available for the lens stack is not being used economically, unnecessarily limiting the performance of the module.

The above disclosures do only describe single aspects, such as focusing or zooming, of the applied electrowetting lenses, which are not sufficient for compact high-resolution imaging systems as applied in e.g. mobile camera modules.

None of the above disclosures addresses the problem of achromatisation, which is needed to achieve a good optical colour correction of the imaging lens system.

Both the above mentioned methods for providing an achromatic lens system are not applicable for electrowetting lenses, because in electrowetting lenses the optical power changes with the radius of the meniscus between the two fluid depending on the applied voltage, while the above mentioned methods apply to fixed optical power lenses only.

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